Claim CH541:

Present-day fish and other aquatic organisms could have survived the
Flood. Many freshwater fish can survive in salt water, and many saltwater
fish can tolerate fresh water. The floodwaters may have been layered by
salinity, allowing others to find their preferred habitat.

Source:

Response:

Layering of the floodwaters contradicts the Flood model, which proposes
that the Flood was turbulent enough to stir up sediments on an
incredible scale. The model proposes that the floodwaters became the
present oceans, so all the water flowing into the oceans would have
ensured that they were well mixed. The freshwater fish would have had
no place to find fresh water.

The fact that many fish can tolerate wide ranges in salinity does not
mean that all can. Furthermore, the problem applies to more than
fish. Freshwater invertebrates are commonly used as indicators of the
health of streams. Even a tiny amount of pollution can cause many
species to disappear from the stream.

Aquatic organisms would have more than salinity to worry about, such as
the following:

Heat. All mechanisms proposed to cause the Flood would have
released enough heat to boil the oceans. The deposition of
limestone would release enough heat to boil them again. Meteors and
volcanoes that occurred during the Flood, as implied by their
presence in layers attributed to the Flood by flood geologists,
would probably have boiled them again (Isaak 1998). Woodmorappe
(1996, 140) dismissed the problem of volcanoes but ignored all the
other sources of heat.

Acid. The volcanoes that erupted during the Flood would also have
produced sulfuric acid, enough to lower the pH of the ocean to 2.2,
which would be fatal to almost all marine life (Morton 1998b).

Substrate. Many freshwater and marine invertebrates rely on a
substrate. They anchor themselves on the substrate and rely on
currents to carry their food to them. During the Flood, substrates
would have been uninhabitable at least part of the time, especially
on land. Woodmorappe (1996, 141) suggested floating pumice as a
substrate, but it would float with the currents, so currents would
not bring nutrients to animals on them.

Pressure. The Flood would have caused great fluctuation in sea
pressures. Many deep-sea creatures invariably die from the
decompression when brought to the surface. Other surface animals
would die from too much pressure if forced deep underwater.

Woodmorappe predicted a sudden extinction of fish caused by the Flood.
"[P]resent-day marine life is but an impoverished remnant of that which
had originally been created and had existed before the Flood" (1996,
142). However, the actual pattern of extinction we see shows
convincing disproof of the Flood. Living genera become decreasingly
represented in fossils as one goes deeper in the geological column,
until there are no recent genera in the Triassic, and only about 12
percent of recent genera have any fossil record. Extinct genera
continue back to the Cambrian (Morton 1998a). This pattern exactly
matches what one would expect from evolution. It contradicts a global
flood, which should include modern fish more-or-less uniformly
throughout the flood-deposited sediments.